1. Field of the Invention
The present invention relates to an energy storage device and, more particularly, to an energy storage device, in which a current collector is attached to a cover member for closing a container that contains an electrode assembly therein.
2. Description of the Related Art
A vehicle such as a hybrid car or an electric car using electric power for a drive source or a part of a drive source has received attention in recent years. As a power source for such a vehicle, an energy storage device having a high energy capacity is practically used. Incidentally, the term “energy storage device” is used as the idea encompassing both of a battery (such as a lithium ion battery or a nickel metal hydride battery) and a capacitor (such as an electric double layer capacitor) in the present specification and claims.
In particular, as an energy storage device to be mounted on an automobile requiring a flow of a large current, a nonaqueous electrolyte secondary battery is used. The nonaqueous electrolyte secondary battery includes a casing constituted of a rectangular thin container and a cover member for closing the container, and an electrode assembly occupying almost all of the inside volume of the casing. In such a secondary battery, an electrode terminal is attached at the outside surface of the cover member. The casing houses a current collector for connecting the electrode terminal and the electrode assembly to each other. The current collector is adapted to take electric power from the electrode assembly to the outside of the casing, and further, to supply the electric power to the electrode assembly.
Moreover, the current collector is physically fixed to the cover member via an insulating member, and further, is electrically and physically connected to the end of the electrode assembly. As a consequence, the electrode assembly is designed to be physically fixed to the cover member via the current collector, and further, to be able to supply and give the electric power in the insulating state with respect to the casing.
In fabricating the above-described secondary battery, it is necessary to definitely determine the position of the current collector with respect to the cover member with ease. A secondary battery disclosed in JP-A-2010-212240 determines the position of a current collector via an insulator by fitting a cover member and an insulating member to each other in position, and further, fitting the insulating member and a current collector to each other.
However, a current collector may be physically fixed to a cover member using a rivet. When the current collector and the cover member are fixed to each other by crushing the rivet, a tool head abutting against the rivet is turned on an axis in a press direction while the rivet is crushed. In this case, the current collector and the cover member produce force to turn in a direction reverse to the turn direction of the tool. The insulating member may not be able to resist the force, and therefore, the current collector and the cover member may be deviated from each other. When deviation occurs between the current collector and the cover member, distortion occurs at the electrode assembly held by the current collector. It is possibility that when the electrode assembly is exposed to vibrations for a long period of time, the electrode assembly is adversely influenced by the deviation or the distortion.